Measuring Rims (What is a rim inner diameter anyway?)

The "inner diameter" is perhaps the single most important aspect of a rim for defining whether it will work for a given player.  But what exactly are we measuring here?  We want to sort of get at the "bite point" of the rim, but where is that anyway?  Should we measure at some known depth?  Some angle?  What about very curvy rims without a defined "bite"?

Since there are many different ways of measuring, unfortunately we get many different results.  Players find that in brand X they need a size Y which differs from their regular brand, etc.  Some of that difference is undoubtedly due to how the player's face interacts with the given rim - you might get two different answers on which rim "feels" bigger from two different players with different facial anatomy, but generally if you asked players to order a group of rims by size you'll get a consistent order by how big they feel.

Fortunately we can use this perceived standard to try to define an actual standard.  When you put out a rim, people will let you know if it's bigger or smaller than their expectations.  No matter how you measured - if you call it an 18 the community will tell you if it's really an 18.

We propose the following then as a standard for measuring the size of the rim:

We set the "loss of contact" point to be the point at which a 60 degree cone touches the rim's surface.  Beyond this point, your lips will be unsupported by the rim and begin the resonating section.  The rim's "inner diameter" then is simply the diameter at this point.

This has some advantages; it's fully objective and it's easy to use while designing a rim - simply fix your splines to intersect the desired inner diameter at a 60 degree angle and you're golden.

It also lets us measure existing rims more easily.  To that end I've printed up a little measuring device.  It has grooves cut out of the side so you can feel which size it is by which grooves the rim runs over.

With this in mind, we have some adjustments to make to the existing lineup's nominal sizing.

The Rim E is now considered not a 17.75 but a 17.5.

The Rim R 18.5 is actually an 18.25.  The other rim Rs are true to size.

The Rim X is not an 18 but an 18.5

Hopefully this helps ensure that rims have a more uniform feeling!